This invention relates to the field of aircraft altitude determination as accomplished electronically from within the considered aircraft by a passive, non signal emitting and global positioning system signal-based technique.
The conventional radar altimeter transmits a radar signal from its host aircraft to the ground and processes a reflected or returned radar signal to determine the altitude of the host aircraft. A transmitted signal of this nature can, however, be detected by hostile persons to reveal the presence of the aircraft and to provide guidance for ordnance intended to intercept the aircraft. Similar non-atmospheric pressure altitude measuring arrangements based on electromagnetic energy of differing wavelengths including, for example, laser energy emissions are possible under some weather conditions but have the related disadvantages of being detectable and providing ordnance target identification. The present invention provides an uncomplicated measurement of aircraft altitude free of these signal emission and target identification disadvantages. The invention employs signals readily available in most parts of the world and makes additional use of some apparatus possibly already available on the host aircraft.